1. Field of the Invention
The present invention relates to a passenger's weight measurement device for vehicle seat, for measuring a weight of a passenger of a vehicle seat, and an attachment structure for attaching a load sensor to the passenger's weight measurement device.
2. Description of the Related Art
Recently, to improve performance of various safety devices such as a seat belt and an air bag, operations of the safety devices have been controlled in accordance with a weight of a passenger sitting on a vehicle seat in some cases. In the conventional passenger's weight measurement device for measuring a weight of a sitting passenger, a load sensor is disposed between a vehicle floor and the vehicle seat (For example, refer to JP A 2004-317285 and U.S. Pat. No. 6,161,891).
However, when the passenger's weight measurement device is assembled, when the vehicle seat is fixed to the passenger's weight measurement device, and when the passenger's weight measurement device is fixed to the vehicle floor or the like, a dimension error or an assembling position error occurs to cause very low distortion. Because an initial load is applied to the load sensor by the distortion, there is a first problem that it is difficult to accurately measure the passenger's weight.
JP A 11-304579 discloses a passenger's weight measurement device capable of simplifying characteristics of a load applied on a load sensor as much as possible.
The passenger's weight measurement device disclosed in JP A 11-304579 is equipped with a seat connection mechanism which includes an arm disposed to interconnect a seat bracket and a seat of a vehicle and to rotate up and down. The device also includes a load sensor disposed between the vehicle and the seat to detect a seat weight. The arm is pivotally attached to a pivotal shaft (pivot) of the seat side and a pivot of a car body side, and the load sensor selectively receives an up-and-down direction component of the seat weight applied on the arm. According to the passenger's weight measurement device disclosed in JP A 11-304579, displacement of the seat with respect to the vehicle body, which is caused when a load is applied on the seat, has certain regularity, and characteristics of the load applied on the load sensor are simplified, thereby facilitating capturing of the passenger's weight on the seat.
According to the passenger's weight measurement device disclosed in JP A 11-304579, seat adjusters project from four positions, front, back, left and right, of a bottom surface of a seat cushion on which the passenger sits. The seat adjuster is a portion of which a seat frame partially projects, and can slide back and forth on a pair of seat rails by passenger's adjustment. The seat adjuster and the seat rails constitute a so-called slide rail. However, the passenger's weight measurement device disclosed in JP A 11-304579 has a problem that the large number of components such as a linking member is increased because the pair of slide rails and the seat bracket fixed to the vehicle body floor side are linked together by a parallelogram linking mechanism. Because the parallelogram linking mechanism is disposed between the pair of slide rails and the seat bracket, there is a problem that it is difficult to set a height from the vehicle body floor to an upper surface of the seat cushion equal to or less than a certain height.
To solve the aforementioned problems, a plurality of compression type load cells (load sensors) are disposed between the pair of slide rails arranged on the vehicle body floor side and the pair of side frames for supporting the seat. Thus, the configuration is simplified and the restrictions on the height from the vehicle body floor to the upper surface of the seat cushion are eliminated. However, generally it is difficult to accurately fix the pair of slide rails and the like to the vehicle body floor side. Further, it is difficult to maintain a facing distance between the pair of side frames because of the seat sliding. In this structure, there is a second problem that an unnecessary force is applied on the load cell to interfere with passenger's load measurement.